1. Field of the Invention
The present invention relates to a method of preparing barium fluoroiodide, and specifically to a method of preparing barium fluoroiodide as a phosphor materials.
2. Description of the Related Art
Conventionally, a bivalent europium-activated barium fluorohalide phosphor (BaFX:Eu2 +; wherein X is Cl, Br and/or I) has been known as a phosphor for a radiation image conversion panel used for radiography projection. This phosphor emits light (instantaneous emission of light) in a near-infrared region, which emission has an emission maximum close to 390 nm, when excited with radiation such as an X-ray, electron beam, ultraviolet ray, or the like.
Further, it has been found that, if the above-described phosphor is exposed to the above-mentioned radiation, and then excited with electromagnetic waves (excitation light) in a range from a visible region to an infrared region, the phosphor emits light in a near-ultraviolet region; i.e., stimulated emission. As disclosed in Japanese Patent Application Laid-Open (JP-A) No. 55-12145 and the like, the phosphor has been especially noted as a phosphor for a radiation image conversion panel used in a radiation image conversion method which utilizes stimulability of the phosphor. Of such phosphors, bivalent europium-activated barium fluoroiodide phosphor (BaFI:Eu2 +) emits longer wavelenth light whose wavelength is in the longer wavelength side. Accordingly, it has been proposed that this phosphor be used in combination with semiconductor laser light which serves as excitation light and whose oscillation wavelength is in a near-ultraviolet region.
Barium fluoroiodide (BaFI) is used as a material (a so-called phosphor powder) for manufacturing the aforementioned bivalent europium-activated barium fluoroiodide phosphor or a bivalent europium-activated iodine-containing barium halide phosphor.
Japanese Patent Application No. 60-243613, filed by the applicant of the present invention, discloses a method to obtain a barium fluorohalide. In this method, at least one compound, which is selected from the group consisting of carbonate, nitrate and sulfate which are salts of barium is reacted with at least one compound selected from the group consisting of hydrogen chloride, hydrogen bromide and hydrogen fluoride to generate a barium halide. Then the resultant product is reacted with hydrogen fluoride to generate the barium fluorohalide. However, barium fluoroiodide, unlike barium fluorobromide and the like, has a high solubility with respect to water. Therefore, the product cannot be obtained with a sufficiently high yield simply by reacting the materials in an aqueous medium. Further, there is a problem in that it is easy for impurities to be mixed in.
An object of the present invention is to provide a method of preparing barium fluoroiodide in which barium fluoroiodide having high purity can be obtained with high yield. Another object of the present invention is to provide an iodine-containing barium fluorohalide phosphor in which the barium fluoroiodide obtained by the above-mentioned method is used as at least one of materials for the phosphor, and a radiation image conversion panel in which the iodine-containing barium fluorohalide phosphor is used.
The above-described objects are accomplished by the present invention. That is to say, a first aspect of the present invention is a method of preparing barium fluoroiodide comprising the steps of: (a) mixing barium carbonate with an aqueous solution of hydrogen iodide in a molar ratio from 0.5 to 2 of hydrogen iodide to barium carbonate, and concentrating the resultant solution to prepare a suspension having barium iodide dissolved in the solution at a concentration of at least 3.0 mol/l; (b) precipitating barium fluoroiodide by adding a total amount of hydrogen fluoride to the suspension to achieve a molar ratio from 0.4 to 0.8 of hydrogen iodide to the barium carbonate, and wherein the hydrogen fluoride is added at a rate to generate 0.001 N/minute to 10 N/minute of barium fluoroiodide precipitate, wherein N is the theoretical amount of barium fluoroiodide precipitate that can be generated based upon the amount of barium carbonate in the suspension; and (c) separating the precipitate.
In the claim 1, (a) may be referred to as a suspension preparing step, (b) may be referred to as a precipitate generating step, and (c) may be referred to as a precipitate separating step.
A second aspect of the present invention is an iodine-containing barium fluorohalide phosphor, which is prepared by using, as at least one of materials for preparation therefor, barium fluoroiodide obtained by the method of preparing barium fluoroiodide comprising the steps of: (a) mixing barium carbonate with an aqueous solution of hydrogen iodide in a molar ratio from 0.5 to 2 of hydrogen iodide to barium carbonate, and concentrating the resultant solution to prepare a suspension having barium iodide dissolved in the solution at a concentration of at least 3.0 mol/l; (b) precipitating barium fluoroiodide by adding a total amount of hydrogen fluoride to the suspension to achieve a molar ratio from 0.4 to 0.8 of hydrogen iodide to the barium carbonate, and wherein the hydrogen fluoride is added at a rate to generate 0.001 N/minute to 10 N/minute of barium fluoroiodide precipitate, wherein N is the theoretical amount of barium fluoroiodide precipitate that can be generated based upon the amount of barium carbonate in the suspension; and (c) separating the precipitate.
A third aspect of the present invention is a radiation image conversion panel which is formed such that a phosphor layer contains at least the iodine-containing barium fluorohalide phosphor prepared by using, at least one of materials for preparation therefor, barium fluoroiodide obtained by the method of preparing barium fluoroiodide comprising the steps of: (a) mixing barium carbonate with an aqueous solution of hydrogen iodide in a molar ratio from 0.5 to 2 of hydrogen iodide to barium carbonate, and concentrating the resultant solution to prepare a suspension having barium iodide dissolved in the solution at a concentration of at least 3.0 mol/l; (b) precipitating barium fluoroiodide by adding a total amount of hydrogen fluoride to the suspension to achieve a molar ratio from 0.4 to 0.8 of hydrogen iodide to the barium carbonate, and wherein the hydrogen fluoride is added at a rate to generate 0.001 N/minute to 10 N/minute of barium fluoroiodide precipitate, wherein N is the theoretical amount of barium fluoroiodide precipitate that can be generated based upon the amount of barium carbonate in the suspension; and (c) separating the precipitate.